1. Field of the Invention
The present invention relates generally to the fields of neuroendocrinology and neuropeptide chemistry. More specifically, the instant invention relates to protein factors involved in the regulation of neuroendocrine and paracrine responses to stress. Most specifically, the present invention discloses a corticotropin releasing factor related peptide designated urocortin III.
2. Description of the Related Art
Corticotropin releasing factor (CRF) and its related family of peptides were recognized initially for their regulation of the hypothalamic-pituitary-adrenal axis (HPA) under basal and stress conditions (1, 2). Corticotropin releasing factor (CRF) is a 41 amino acid peptide that was first isolated from ovine hypothalamus (3) and shown to play an important role in the regulation of the pituitary-adrenal axis, and in endocrine, autonomic and behavioral responses to stress (4). The CRF family of neuropeptides also includes structurally related mammalian and non-mammalian peptides such as urocortin (Ucn), a 40 amino acid peptide originally identified in rat brain (5), fish urotensin I (Uro) (6), and amphibian sauvagine (Svg) (7).
It has been hypothesized that members of the CRF family are involved in neuroendocrine and paracrine responses in many tissues. In addition to their effects on the pituitary and central nervous system, members of the CRF family have been shown to modulate cardiovascular and gastrointestinal functions and inflammatory processes in mammals to integrate endocrine, autonomic and behavioral responses to stressors. These peptides may also be implicated in the control of appetite, arousal, and cognitive functions. Severe psychological and physiological consequences can occur as a result of the long term effects of stress, such as anxiety disorders, anorexia nervosa, gastrointestinal dysfunction and melancholic depression.
CRF family members mediate their biological actions by specifically binding to CRF receptors with high affinities (8, 9). CRF receptors are G-protein coupled receptors that act through adenylate cyclase and are structurally related to the secretin receptor family. This family also includes GRF, VIP, PTH, and the calcitonin receptors.
The CRF receptors are derived from two distinct genes, CRF receptor type 1 (CRF-R1) (10-12) and CRF receptor type 2 (CRF-R2) (13-15). CRF-R1 and CRF-R2 have distinct pharmacologies and differ in their anatomical distribution (16). The type 1 CRF receptor (CRF-R1) gene has 13 exons; several splice variants of this receptor have been found. The CRF-R1 is distributed throughout the brain and is found in sensory and motor relay sites (17). The rodent type 2α receptor (CRF-R2α) is distributed in lateral septum, ventral medial hypothalamus, nucleus of the solitary tract and the dorsal raphe nucleus, which are areas where CRF-R1 is expressed very little or not at all (18). The rodent type 213 receptor (CRF-R2β) is found mostly in peripheral sites including the heart, blood vessels, gastrointestinal tract, epididymis, lung and skin (9, 19).
The pharmacology of the two types of receptors differs in that CRF has a modest affinity for CRF-R2 [Ki=5-100 nM] but high affinity for CRF-R1 [Ki=1-2 nM]. Other related peptides such as carp urotensin, frog sauvagine, and urocortin have a high affinity for both CRF-R1 and CRF-R2. CRF-R2 knockout mice demonstrate an increased anxiety-like behavior caused by hypersensitivity to stressors (5, 20).
Recently, searches of the public human genome database identified a region with significant sequence homology to the CRF neuropeptide family. The entire human sequence was amplified and sequenced. The human sequence, however, lacks a consensus proteolytic cleavage site that would allow for C-terminal processing of the peptide, and is therefore referred to as an urocortin-related peptide (URP) sequence. Using homologous primers deduced from the human sequence, a mouse cDNA was isolated from whole brain poly (A+) RNA that encodes a predicted 38 amino acid peptide, designated urocortin II, which is structurally related to the other known mammalian family members, CRF and urocortin (Ucn). The question of whether human urocortin-related peptide represents the mouse Ucn II ortholog remains open until additional mouse genes are identified. Ucn II binds selectively to the type 2 CRF receptor (CRF-R2), with no appreciable activity on CRF-R1. Transcripts encoding Ucn II are expressed in discrete regions of the rodent CNS, including stress-related cell groups in the hypothalamus (paraventricular and arcuate nuclei) and brainstem (locus coeruleus). These findings identify Ucn II as a new member of the CRF family of neuropeptides, which is expressed centrally and binds selectively to CRF-R2. Initial functional studies are consistent with Ucn II involvement in central autonomic and appetitive control, but not in generalized behavioral activation (21).
The prior art is deficient in the recognition of the human Urocortin-III gene and protein and uses thereof. The present invention fulfills this longstanding need and desire in the art.